1. Field of the Invention
The present invention relates to a motor control apparatus and more particularly to a motor control apparatus for controlling a motor in response to a switch operation.
2. Related Art
Conventionally, there is suggested a power window system in which a microcomputer controls a relay and the like in response to a switch operation so as to drive a motor.
In the power window system, there is the possibility that an open and close operation of the power window cannot be controlled due to the microcomputer becoming uncontrollable and the like, which is inconvenient. In order to prevent this, control of a microcomputer by using a watchdog circuit has been proposed. However, since the watchdog circuit can only restart the microcomputer but cannot control an operation signal when the switch is operated, when the runaway of the microcomputer is maintained, the motor cannot be controlled and the convenience of the system deteriorates.
In order to prevent this problem, there is suggested a power window system having a multiplex control system comprising a microcomputer control system and a switch control system in which a motor can be controlled by either the microcomputer control system or the switch control system in response to a switch operation. In the power window system, whether the microcomputer control system is in a normal state is judged by determining whether a clock signal is output from the microcomputer control system at each time a predetermined period of time passes of time passes by the microcomputer in the switch control system. Then, the microcomputer in the switch control system controls a switch device in such a manner that if the microcomputer control system is in a normal state, the motor is controlled by a signal from the microcomputer control system and if the microcomputer control system is not in a normal state, the motor is directly controlled by a switch operation.
However, since in the power window system having a multiplex control system, the microcomputer in the switch control system controls the switch device so as to switch the system between the microcomputer control system and the switch control system, if both of the microcomputers in the microcomputer control system and the switch control system run away, it is difficult to directly control the motor by the switch operation so that the convenience of the system deteriorates.